Pinto Gneiss

The banded and folded Pinto gneiss, approximately 1.7 billion years old, is most likely the
oldest type of rock in the park. Gneiss, a metamorphic rock, has undergone change
in mineral composition, grain size and orientation due to increases in pressure, heat and
chemical activity. Gneiss, prior to its change, was a sedimentary rock. With directed pressure,
mineral grains segregate and band together; this alternate banding of light and dark minerals
is what defines a gneiss.

Pinto Gneiss

Lichens

Brightly colored splotches found on the gneiss are a primitive form of plant life called
lichens. Lichens are a mutually beneficial composite of fungi and algae. The various colors
indicate different species. Some species form a weak carbonic acid, the primary agent in
the chemical breakdown of rock into soil.